Certain heterostructure materials, such as Aluminum Gallium Nitride (AlGaN) and Gallium Nitride (GaN), create an electron well (i.e., a sheet of electrons) at the interface between the two dissimilar materials resulting from the piezoelectric effect and spontaneous polarization effect therebetween. The resulting sheet of electrons that forms at this interface is typically referred to as a Two-Dimensional Electron Gas (“2DEG”) channel. An equally applicable heterostructure could have a plurality of two-dimensional hole gas (2DHG) channels. Both types of heterostructures can be referred to as “2DxG channel(s)” devices. FETs that operate by generating and controlling the electrons in the 2DxG channel are conventionally referred to as high electron mobility transistors (“HEMTs”). Typical GaN HEMTs will be conductive when zero volts is applied to the gate (also called “normally on”), and require a negative gate bias to turn them off. This type of operation is known as depletion mode, or d-mode, operation. However, many applications require a device which is non-conductive when zero volts is applied to the gate (“normally off”), with a positive gate bias required to turn them on. This mode of operation is known as enhancement mode, or e-mode, operation.
Typically, GaN circuits interface with silicon-based complimentary metal oxide semiconductor (CMOS) devices to provide both d-mode and e-mode operation in the same module. Operation of Silicon (Si) CMOS circuitry with GaN HEMT devices currently requires the use of level shifters due to the differing polarity and magnitude of gate voltages employed on the Si and GaN devices. These level shifters could be eliminated if the e-mode devices could be implemented in the GaN circuits. Furthermore, recent schemes in DC-DC power conversion involve class E amplifiers driven by d-mode HEMTs with drain voltages modulated by buck converters that are, by necessity, also driven by d-mode HEMTs. These buck converters could operate more efficiently with e-mode HEMTs.